The present invention pertains to a system, method, and device for treating sleep disorders. The present invention is particularly useful in the delivery of carbon dioxide (CO2) to a subject and in the treatment of sleep apnea. In various embodiments of the present invention where components are integrated as a rebreathing circuit, a subject is the source and recipient of a controlled volume of a specific concentration of carbon dioxide. In such embodiments, when at least one component is a positive airway pressure device, ventilator, or the like, treatment of sleep disorders becomes much more efficient and effective.
Nearly one in seven people in the United States suffer from some type of chronic sleep disorder, and only 50% of people are estimated to get the recommended seven to eight hours of sleep each night. It is further estimated that sleep deprivation and its associated medical and social costs (loss of productivity, industrial accidents, etc.) exceed $150 billion per year. Excessive sleepiness can deteriorate quality of life and is a major cause of morbidity and mortality due to its role in industrial and transportation accidents. Sleepiness further has undesirable effects on motor vehicle driving, employment, higher earning and job promotion opportunities, education, recreation, and personal life.
Primary sleep disorders affect approximately 50 million Americans of all ages and include narcolepsy, restless legs/periodic leg movement, insomnia, and most commonly, sleep apnea. Sleep apnea is defined as the cessation of breathing during sleep. Hundreds of episodes of apnea may occur in one night, lasting 10 seconds or longer, thereby disrupting sleep. The three major types of sleep apnea are obstructive sleep apnea (OSA), central sleep apnea (CSA), and complex sleep apnea (CompSA). The prevalence of OSA in society is comparable with diabetes, asthma, and the lifetime risk of colon cancer. OSA is grossly under diagnosed; an estimated 80-90% of persons afflicted have not received a clinical diagnosis. OSA is characterized by repetitive pauses in breathing during sleep due to the obstruction and/or collapse of the upper airways, usually accompanied by a reduction in blood oxygen saturation. Despite obstructions, respiratory effort continues during the episodes of OSA. In contrast to OSA, where the central nervous system continues to drive respiratory effort but a physical blockage prevents inhalation of oxygen, CSA is a neurological condition resulting in the cessation of respiratory effort during sleep.
Although the effects of OSA and CSA are highly similar, effective treatment can differ because the physical cause of OSA is very different from the neurological mechanism behind CSA. Because the treatments of OSA and CSA vary substantially, proper diagnosis of the correct type of sleep apnea is critical for an effective treatment. The most common method of treating OSA is the use of positive airway pressure (PAP), generated by a PAP device. PAP treatment is most commonly conducted with the subject wearing an oronasal mask or similar apparatus that is connected to a PAP device via a hose that can deliver the pressurized air generated by the PAP device to the subject's airway. When using a standard PAP device to treat OSA, the positive airway pressure generated by the PAP device acts as a splint, holding the airway open and reducing or removing the obstruction. With continuous positive airway pressure (CPAP) treatment, an optimal pressure is determined by a sleep technician during a titration period in which the positive pressure provided by the CPAP is adjusted until a pressure sufficient to maintain airway patency is found and thus reduces the number of apneic events experienced by the subject being treated. Once the optimal pressure is determined, the device is programmed to consistently provide this pressure, and the patient is sent home.
Slightly more advanced PAP devices automatically adjust the air pressure based on sensory feedback mechanisms built into the device. The sensors measure gas flow, pressure, or other fluid characteristics in the device, mask, or both and adjust the delivered pressure based on various algorithms known in the art. Additionally, these auto-PAP devices predict or detect an apnea event by measuring a subject's exhaled air using similar sensors. The many variations of PAP devices are generally referred to as PAP devices, with specific variations noted where appropriate.
Subjects with CompSA are characterized by the emergence of CSA events after the application of PAP therapy. CompSA can be thought of as a combination of OSA and CSA. Current PAP devices are insufficient for the treatment of CSA or CompSA because the delivered pressure is only able to combat airway obstructions rather than the neurological condition disrupting respiratory effort associated with central sleep apnea. While pressure cannot combat CompSA or CSA, physiologically excess carbon dioxide induces chemoreceptors to signal the nervous system to increase respiratory effort drive. U.S. Pat. No. 7,886,740 to Thomas et al., issued Feb. 15, 2011, adds low concentrations of carbon dioxide from an external CO2 source to the delivered pressurized air from a PAP device and delivers the mixture to a subject. The addition of CO2 from an external source, however, requires additional tubing, machinery (such as a cart), and another point of maintenance for the subject when the CO2 supply is exhausted or machinery fails. Thomas additionally discusses using a variable deadspace mask which would cause the patient to rebreathe his own CO2 that accumulates in the mask. However, these embodiments struggle to control proper CO2 levels in the mask and during inspiration when mixed with air from a PAP device.
It is therefore an object of the present invention to provide an effective means of treating sleep disorders, particularly sleep related breathing disorders by providing CO2 to a subject in controlled quantities. It is another object of the present invention to increase patient comfort and treatment effectiveness by using a subject's exhaled air as a source of CO2, particularly through a rebreathing circuit. It is still another object of the present invention to actively control CO2 concentrations delivered to a subject based on physical properties measured from air in the rebreathing circuit. It is still another object of the present invention to actively control CO2 concentrations delivered to a subject based on physiological signals measured from the subject. It is still another object of the present invention to treat a subject's apnea in a manner predictive of the subject's breathing patterns. It is still another object of the present invention to provide a device and method of controlling levels of CO2 delivered to a subject in the subject's home. It is still another object of the present invention to provide a device and method of controlling levels of CO2 delivered to a subject in a hospital's acute or sub-acute settings, such as for postoperative management of care.